Amorphous content

The difference between 1.0 and the sum of the as-received components represents the total amount of amorphous material in the sample and/or non-included phases in the analysis and can be calculated from  

Note that Equation (AlO) is only summed over n — 1 phases since the internal standard phase is now omitted from the calculation. 

Chung and D. K. Smith, in Industrial Applications of X-Ray Diffraction, ed. F. H. Chung and D. K. Smith, Marcel Dekker, New York, 2000. 

King and F. E. Alexander, X-Ray Diffraction Procedures, Wiley-Interscience, New York, 1974. 

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The loop formed by the chain as it emerges from the crystal, turns around, and reenters the crystal may be regarded as amorphous polymer, but is insufficient to account for the total amorphous content of most crystalline polymers. 

The decrease in amorphous content follows an S-shaped curve. The corresponding curve for the growth of crystallinity would show a complementary but increasing plot. This aspect of the Avrami equation was noted in connection with the discussion of Eq. (4.24). 

The crystallinity in PET soft drink bottles is about 25%. Because a more crystalline state is normal for PET, the amorphous content is increased intentionally by copolymerization and rapid cooling for the molten PET from the melt to a temperature below the glass transition temperature. Companies which perform high-speed blow molding of PET prefer PET resins made with small amounts of glycol and diacid comonomers. 

Polymer material/product characterisation crystallinity, amorphous content, phase analysis WAXS, WAXD, SAXS, SALLS, density, DSC, IR, Raman, s-NMR, AFM, optical microscopy, SEM, TEM... 

Figure 5 Raman spectra of orthorhombic ethylene 1-hexene copolymer with band fitting. The crystalline band at 1,416 cm-1, and amorphous bands at 1,303 cm- and 1,080 cm- are used to compute the crystallinity content ac = 0.52, and the amorphous content aa = 0.42. (See Color Plate Section at the end of this book.)...

Figure 10 Degree of crystallinity from WAXS, interfacial content from PALS and amorphous content from PALS for an ethylene 1-octene copolymers as a function of increasing 1-octene. Reproduced with permission from Ref. [158]. Copyright 2002 Elsevier Ltd.

The technique appears to be particularly useful in the characterization of glass transition phenomena. The utility of MDSC in the study of glass transitions can lead to methods for determination of the amorphous content in a substance [62,63]. 

Amorphous cellulose, so defined, was reported for two simple but noteworthy modifications of cotton linters. First, linters which had been swollen with cold 10% sodium hydroxide, washed, and dried by solvent exchange prior to thallation and methylation, showed an amorphous content as high as 27 %. Secondly, unswollen linters appeared to contain only 0.25 to 0.50% of amorphous cellulose. Similarly, swollen ramie appeared to contain 18% of amorphous cellulose unswollen ramie, 0.25%. 

Cheng, S. Z. D., Pan, R. and Wunderlich, B Thermal analysis of polybutylene terephthalate for heat capacity, rigid-amorphous content, and transition behavior, Makromol. Chem., 189, 2443-2458 (1988). 

We have found by examining the spectrum for the solution-grown samples at room temperature that their phase structure is composed of lamellalike crystallites and an amorphous overlayer having limited molecular mobility, with a very small amount of liquidlike amorphous content. This unique phase structure is reflected in more detail in the temperature dependence of the spectrum. 

The reaction is exothermic and may form polymer from a molecular weight of 1000 to well over 1 million. The high-pressure process, which normally produces types I and II, uses oxygen, peroxide, or other strong oxidizers as catalyst. Pressure of reaction ranges from 15.000 to 50.000 psi ( 1,020-3,400 atmospheres). The polymer formed in this process is highly branched, with side branches occurring every 15-40 carbon atoms on the. chain backbone. Ciystallinity of this polyethylene is approximately 40-60%, Amorphous content of the polymer increases as the density rs reduced,... 

Fig. 5. Calculation of the amorphous content of polytetrafluoroethylene from the x-ray diffraction pattern. (After Ryland)...

Moynihan made particular use of the band at 778 cm 1 (12.85 ft) for which the absorbance per unit thickness divided by density is proportional to the amorphous content measured by x-ray diffraction. In Fig. 6, it is... 

In recent years there has been increasingly more interest in determining the amorphous content of pharmaceutical materials. This is due to... 

For formulated products an essential analysis is the assay for API content. This is usually performed by HPLC, but Raman spectroscopy can offer a quantitative analytical alternative. These applications have been extensively researched and reviewed by Strachan et al. [48] and provide over 30 literature references of where Raman spectroscopy has been used to determine the chemical content and physical form of API in solid dosage formulations. As no sample preparation is required the determination of multiple API forms (e.g. polymorphs, hydrates/solvates and amorphous content) provides a solid state analysis that is not possible by HPLC. However, as previously discussed sampling strategies must be employed to ensure the Raman measurement is representative of the whole sample. A potential solution is to sample the whole of a solid dosage form and not multiple regions of it. As presented in Chap. 3 the emerging technique of transmission Raman provides a method to do just this. With acquisition times in the order of seconds, this approach offers an alternative to HPLC and NIR analyses and is also applicable to tablet and capsule analysis in a PAT environment. 

Savolainen et al. investigated the role of Raman spectroscopy for monitoring amorphous content and compared the performance with that of NIR spectroscopy [41], Partial least squares (PLS) models in combination with several data pre-processing methods were employed. The prediction error for an independent test set was in the range of 2-3% for both NIR and Raman spectroscopy for amorphous and crystalline a-lactose monohydrate. The authors concluded that both techniques are useful for quantifying amorphous content however, the performance depends on process unit operation. Rantanen et al. performed a similar study of anhydrate/hydrate powder mixtures of nitrofurantoin, theophyllin, caffeine and carbamazepine [42], They found that both NIR and Raman performed well and that multivariate evaluation not always improves the evaluation in the case of Raman data. Santesson et al. demonstrated in situ Raman monitoring of crystallisation in acoustically levitated nanolitre drops [43]. Indomethazine and benzamide were used as model... 

Crystallinity refers to a regular, ordered, three-dimensional crystal lattice portion of a polymer (Kroschwitz, 1990) where the polymer chains align themselves in perfect parallel array. There are no purely crystalline polymers, as all polymers, even so-called crystalline polymers, have some portion of amorphous content. Nonetheless, crystalline regions of polymers can form up to 98% of the polymer structure (Rosen, 1993) and have consequent large impacts on mechanical behavior. 

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